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1.
Spontaneous emission and spectral properties of radiation by relativistic electrons in a gyro‐klystron and optical‐klystron undulator
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In this paper spontaneous emission of radiation by relativistic electrons in a gyro‐klystron is studied. The scheme consists of two solenoid sections separated by a dispersive section. In the dispersive section the electrons are made non‐resonant with the radiation. The dispersive section transforms a small change of the velocity into changes of the phases of the electrons. This leads to enhanced radiation due to klystron‐type modulation as compared with a conventional gyrotron‐type device driven by cyclotron maser interaction. It is shown that the klystron‐modulated spectrum depends on the dispersive field strength, finite perpendicular velocity component and length of the solenoids but is independent of the axial magnetic field strength. A simple scheme to design a gyro‐klystron is discussed. 相似文献
2.
The question at stake is, whether a simple physical connection may be found between Richardson equation for thermionic emission on the one hand, and Richardson equation for photoelectric emission on the other hand. The proposition of such a connection is based on the following supposition: that electrons are not only elements of a (Fermi-Dirac-) statistical ensemble and, as such, cause thermionic phenomena; but that they can also interact with a radiation field, thereby causing an additional emission current, according to Richardson (photoelectric) equation. — It is shown in detail that the current emitted from a metal of 2000 °K is determined by the complete radiation of this metal only to a very slight degree. It is then estimated however, that within temperatures of some million degrees Kelvin the excitation of electrons caused by complete radiation will be much greater than that caused by interaction. 相似文献
3.
Radiation damping effects on the interaction of ultraintense laser pulses with an overdense plasma 总被引:1,自引:0,他引:1
A strong effect of radiation damping on the interaction of an ultraintense laser pulse with an overdense plasma slab is found and studied via a relativistic particle-in-cell simulation including ionization. Hot electrons generated by the irradiation of a laser pulse with a radiance of I lambda(2)>10(22) W microm(2)/cm(2) and duration of 20 fs can convert more than 35% of the laser energy to radiation. This incoherent x-ray emission lasts for only the pulse duration and can be intense. The radiation efficiency is shown to increase nonlinearly with laser intensity. Similar to cyclotron radiation, the radiation damping may restrain the maximal energy of relativistic electrons in ultraintense-laser-produced plasmas. 相似文献
4.
超短超强激光与固体靶相互作用,可以产生大量的Kα特征谱线发射。这种Kα线光源在背光照相、医学成像和超快诊断等方面具有显著优势。为了寻求获得Kα线高产额的方法,利用ITS蒙卡模拟程序,对超短超强激光产生的超热电子在固体靶中产生的Kα线发射进行了模拟。系统研究了Kα线发射强度随出射角度、靶厚度和超热电子温度等参数的变化情况。研究发现在恒定的激光功率密度或超热电子温度下,存在最佳的靶厚度,使得Kα线光子产额最大,并用模拟结果对已有实验数据进行了解释。 相似文献
5.
V. A. Shalygin L. E. Vorobjev D. A. Firsov A. N. Sofronov G. A. Melentyev M. Ya. Vinnichenko V. V. Lundin A. E. Nikolaev A. V. Sakharov A. F. Tsatsul’nikov 《Bulletin of the Russian Academy of Sciences: Physics》2012,76(2):207-210
The emission of terahertz radiation from a AlGaN/GaN heterostructure under the heating of two-dimensional electrons in a lateral
electric field is studied. The field dependence of the temperature of hot electrons is determined from an analysis of experimental
volt-ampere characteristics. A theoretical model of the thermal radiation of hot two-dimensional electrons is considered,
and the calculation results are compared with an experiment on terahertz radiation emission. 相似文献
6.
The absorption of terahertz radiation by free charge carriers in n-type semiconductor quantum wells accompanied by the interaction of electrons with acoustic and optical phonons is studied.
It is shown that intrasubband optical transitions can cause both heating and cooling of the electron gas. The cooling of charge
carriers occurs in a certain temperature and radiation frequency region where light is most efficiently absorbed due to intrasubband
transitions with emission of optical phonons. In GaAs quantum wells, the optical cooling of electrons occurs most efficiently
at liquid nitrogen temperatures, while cooling is possible even at room temperature in GaN heterostructures. 相似文献
7.
8.
Cyclotron mechanism of free-electron lasing without inversion 总被引:1,自引:0,他引:1
We consider one of the “paradoxical” effects of the theory of radiation and matter interaction: stimulated emission in the absence of inversion. The theory of simultaneous inversionless emission of two high-frequency waves due to their parametric interaction with ensemble of free electrons in magnetic field is developed. The analytical investigation and numerical simulation of the most interesting scheme of this two-photon interaction are presented. New effects are revealed; namely they are self-induced parametric instability of sufficiently strong waves and enhanced parametric instability in sufficiently dense electron medium. 相似文献
9.
Vnukov I. E. Kalinin V. N. Naumenko G. A. Padalko D. V. Potylitsyn A. P. 《Russian Physics Journal》2001,44(3):263-275
A simple model for calculating the contribution of diffraction of actual photons to the measured spectrum of parametric x radiation (PXR) from relativistic electrons in mosaic crystals is suggested. It is shown that the diffraction of real photons of bremsstrahlung and transition radiation in mosaic crystals whose thickness t is about 0.01 of the radiation length makes a significant contribution to the measurable emission spectrum. The spectra and angular distributions of PXR from electrons with energies 500 and 900 MeV have been measured in mosaic pyrolytic graphite crystals. It is demonstrated that with consideration of diffraction of actual photons in the mosaic crystal, including diffraction of PXR photons, all experimental data presently available agree well with the results of calculations for the suggested model. 相似文献
10.
W. Becker 《Optics Communications》1980,33(1):69-74
A model of the free electron laser is proposed which is based on the classical current of the electron in the wiggler field interacting with a quantized radiation field. To calculate the gain, the quantum recoil for the processes of n-photon emission and absorption must be put in by hand from kinematical considerations. Apart from a spontaneous emission term the gain agrees essentially with the usual small signal expression, for the radiation field being in either an eigenstate of photon number or in a coherent state. The distribution of the electrons after the interaction is, however, essentially quantum mechanical. 相似文献
11.
Corde S Phuoc KT Fitour R Faure J Tafzi A Goddet JP Malka V Rousse A 《Physical review letters》2011,107(25):255003
The features of Betatron x-ray emission produced in a laser-plasma accelerator are closely linked to the properties of the relativistic electrons which are at the origin of the radiation. While in interaction regimes explored previously the source was by nature unstable, following the fluctuations of the electron beam, we demonstrate in this Letter the possibility to generate x-ray Betatron radiation with controlled and reproducible features, allowing fine studies of its properties. To do so, Betatron radiation is produced using monoenergetic electrons with tunable energies from a laser-plasma accelerator with colliding pulse injection [J. Faure et al., Nature (London) 444, 737 (2006)]. The presented study provides evidence of the correlations between electrons and x-rays, and the obtained results open significant perspectives toward the production of a stable and controlled femtosecond Betatron x-ray source in the keV range. 相似文献
12.
The results of a theoretical analysis of the generation of broadband radiation in the infrared and terahertz spectral ranges
upon the excitation of plasma in air by two femtosecond pulses at the fundamental and second-harmonic frequencies of a Ti-sapphire
laser are presented. It is found that the appearance of long-wavelength radiation in a strong field of pulses of different
frequencies can be described in terms of strongly anharmonic oscillations of optical electrons, whereby electrons are pulled
far away from their atoms; these oscillations are accompanied by cascade transitions of electrons from their ground state
to a bound excited state, followed by a transition to the continuum. It is shown that the generated infrared and terahertz
radiation appears in the form of pulses containing a few oscillations of the light field. The efficiency of terahertz generation
varies periodically with an increase in the interaction length of the femtosecond pulses of different frequencies. 相似文献
13.
14.
The oscillatory motion of electrons in a periodic potential under a constant applied electric field, known as Bloch oscillations (BO), is one of the most striking and intriguing quantum effects and was predicted more than eighty years ago. Oscillating electrons emit electromagnetic radiation and here we consider this BO effect for emission in the THz region. To date, it has been assumed that the Bloch oscillation of an electron is anharmonic oscillation, therefore with radiation emitted at the single Bloch frequency. We analyze scenarios when Bloch oscillations can be accompanied by the emission of radiation not only at the Bloch frequency but also with double and triple Bloch frequencies. The first scenario means that electrons could jump over neighboring Stark states. The second scenario of anharmonic emission is coupled to an opening of the minigap in the miniband. 相似文献
15.
Bastiani S Audebert P Geindre JP Schlegel T Gauthier JC Quoix C Hamoniaux G Grillon G Antonetti A 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》1999,60(3):3439-3442
We have studied the distribution function of the hot electrons produced during the interaction of a 120-fs, 60-mJ, 800-nm wavelength and a p-polarized laser pulse with bilayered Al/Fe targets. The main pulse interacts with a preformed plasma, obtained with a controlled prepulse, whose density gradient scale length has been measured. The electron distribution function is characterized by means of the Kalpha emission of the two materials of the target as a function of the Al-layer thickness. The low-energy region (<50 keV) of the hot-electron distribution function shows no dependency in shape on the gradient scale length, but only a variation in the total number of the generated electrons. The comparison between the experimental results and the particle-in-cell and Monte Carlo calculations of the electron distribution function and the Kalpha emission is gratifying. 相似文献
16.
Zheng J Tanaka KA Sato T Yabuuchi T Kurahashi T Kitagawa Y Kodama R Norimatsu T Yamanaka T 《Physical review letters》2004,92(16):165001
Hot electrons and optical emission are measured from the rear surface of a metallic foil. The spectra of the optical emission in the near infrared region have a sharp spike around the wavelength of the incident laser pulse. The optical emission is ascribed to coherent transition radiation due to microbunching in the hot electron beam. It is found that the optical emission closely correlates with the hot electrons accelerated in resonance absorption. 相似文献
17.
S. S. Belyshev L. Z. Dzhilavyan Yu. N. Pokotilovski 《Bulletin of the Russian Academy of Sciences: Physics》2016,80(5):566-571
The emission of γ-quanta, electrons, and positrons upon the decay of 12N and 12B produced in characteristic targets is calculated within radiation–matter interaction models generated using the GEANT and MCNP simulation software. 相似文献
18.
The interaction of free electrons and free electromagnetic radiation, in the presence of a uniform magnetic field, can result
in stimulated emission or absorption. We analyze the dynamics of single electrons by solving the classical, relativistic Lorentz
force equations of motion in these combined fields. An electron may gain energy from, or lose energy to, the radiation field,
depending crucially on the phase and oscillation frequency of the electron's helical motion within the superposed, circularly
polarized light wave. To first order in the radiation field strength, electrons in a monoenergetic, uniformly distributed
beam become spatially bunched, but there is no net energy change. To second order, however, the beam may experience a gain
or loss of energy, corresponding to attenuation or amplification of radiation. We compare the bunching of this laser process
to the bunching processes involved in 1) the Stanford free-electron laser and 2) the cyclotron maser, and find significant
differences in each case. Our analytic results provide a clear, simple picture of the interaction process, and can be useful
in exploring light amplification in astrophysical magnetic fields, the magnetosphere, or in laboratory devices.
Supported in part by Army Contract No. DASG 60-77-C-0083 and NASA Grant NSG-7490. 相似文献
19.
A. Sagisaka H. Daido S. Nashima S. Orimo K. Ogura M. Mori A. Yogo J. Ma I. Daito A.S. Pirozhkov S.V. Bulanov T.Zh. Esirkepov K. Shimizu M. Hosoda 《Applied physics. B, Lasers and optics》2008,90(3-4):373-377
We have observed simultaneously both the fast proton generation and terahertz (THz) radiation in the laser pulse interaction
with a 5-μm thick titanium target. In order to control the proton acceleration and THz radiation, we have changed the duration
of the amplified spontaneous emission (ASE) preceding the main pulse generated by the high-intensity Ti:sapphire laser. A
fast proton beam with the maximal energy of ∼ 490 keV has been realized by reducing the duration of the ASE. Simultaneously,
an intense emission of THz radiation is observed for various ASE durations. We propose the antenna mechanism for the THz radiation,
according to which the fast electrons moving along the target surface emit the low-frequency electromagnetic wave.
PACS 52.25.Os; 52.38.Kd; 52.50.Jm 相似文献
20.
光强超过10~(22) W/cm~2的极端超强激光将光与物质的相互作用推进到辐射主导区域,激发高能伽马光子辐射,产生明显的辐射反作用力效应.辐射反作用力可以显著影响强场中带电粒子的动力学行为,并从根本上改变了极端强场区域的激光等离子体相互作用规律.如何理解和验证辐射反作用力效应是强场物理研究的核心内容之一.本文结合该方向的国内外研究进展,论述了辐射反作用力的经典形式与强场量子电动力学的理论计算与模拟方法,详细讨论了单粒子在强场中的反射、量子随机辐射、自旋-辐射耦合等效应,介绍了激光等离子体相互作用中的电子冷却、辐射俘获、高效伽马辐射等机制,并给出了目前辐射反作用力效应的实验验证方法与进展.针对自旋在强场量子电动力学方面的效应,介绍了激光加速产生极化粒子源的方法. 相似文献